The present invention relates to a post-processing apparatus, the control method thereof and an image forming system equipped with the aforementioned post-processing apparatus.
There has been a widespread use of multi-functional peripherals composed mainly of a photocopier and further equipped with functions of a printer and facsimile. These multi-functional peripherals are provided with various forms of functions conforming to individual purposes of use for the purpose of realizing various user requirements in recent years. For example, one of the commonly known products is a post-processing apparatus for producing a booklet by a saddle stitching or center folding process, using print sheets as sheets with an image formed thereon by an image forming apparatus. In this type of post-processing apparatus, a prescribed number of sheets ejected from a sheet ejection section through the conveying path inside the apparatus are stacked on a sheet tray in the apparatus, and a bundle of these sheets are processed to form a booklet, in the generality of cases.
Incidentally, when such a booklet is produced, there is demand that questionnaire forms or sheets containing listed corrections of prints in the booklet should be inserted into the booklet as insert sheets. Since the insert sheets are to be placed between pages of the booklet, they are smaller than the external size of the booklet, namely, smaller than half the size of the print sheet. To insert such insert sheets into the booklet, insert sheets have to be placed between pages by manual work after production of the booklet. From the viewpoint of working efficiency improvement, it is required that the insert sheets in the state of being inserted in a booklet should be finished in a series of operations of producing a booklet by a post-processing apparatus.
For example, in one of the methods disclosed in the Japanese Unexamined Patent Application Publication No. 2004-10198, the sheet bundles having the same size are subjected to saddle stitching, whereby a booklet is produced. In the other method disclosed therein, a sheet having a size more than twice the size of a sheet bundle is center-folded to wrap the sheet bundles having the same size, whereby a booklet provided with a cover sheet is formed.
However, when an attempt is made to eject the insert sheet to the sheet tray together with the print sheets as base sheets of the booklet in order to finish the booklet with the insert sheet placed therein, the trailing edge of the next print sheet to be ejected might be located forward on the sheet tray as compared with the leading edge of the last ejected insert sheet. In this case, when the sheet bundle including the print sheet and the insert sheet is aligned, the trailing edge of the print sheet will interfere with the leading edge of the insert sheet, with the result that paper jams will occur or alignment between sheets may not be ensured. To avoid this problem, no process has been taken in the conventional post-processing apparatus to produce a booklet with an insert sheet placed therein.
The technique shown in the Japanese Unexamined Patent Application Publication No. 2004-10198 includes such a description that a plurality of sheets with different sizes are placed on a sheet tray and are subjected to processing, although no method is disclosed to finish a booklet with an insert sheet placed therein. However, according to the method, the position where the sheet is loaded is fixed on the sheet tray. Thus, even when such a method is applied to the case of inserting sheets in a booklet, the aforementioned problem occurs depending on the size of the sheet to be processed.
In view of the problems described above, it is an object of an embodiment of the present invention to finish a booklet with an insert sheet placed between the pages thereof when producing the booklet, by applying the process of saddle stitching or center folding to a print sheet as a sheet ejected from an image forming apparatus.
Incidentally, when finishing a booklet with an insert sheet sandwiched in-between, there are many variations in the finished forms desired by users. In this case, in a series of process of producing a booklet by a post-processing apparatus, the process of center folding or saddle stitching is applied at a prescribed position of the sheet bundle. Thus, when insertion of an insert sheet in such a series of process is taken into account, the finished form desired by the user may not be achieved.
Thus, in view of the problems described above, it is another object of an embodiment of the present invention to make it possible to finish a booklet with an insert sheet placed in-between and to allow the finished forms to be implemented in many variations when producing a booklet by applying the process of saddle stitching or center folding to a print sheet as a sheet ejected from an image forming apparatus.
As is widely known, in the post-processing apparatus, a plurality of sheets fed from the image forming apparatus and having an image formed thereon are aligned and formed in a bundle, and the central portion thereof is stitched by a stapler or others. After that, the bundle is folded at the stitched position and is formed into a booklet, which is then taken out of the apparatus.
In the aforementioned sheet center folding operation, the stitched portion of the sheet is normally pushed into the nip section of folding rollers by a folding knife and the sheet is folded into two parts. Thus, the two-folded portion of center folded sheet bundle faces in the direction of sheet ejection. Accordingly, the sheets are ejected on the tray directly from the sheet ejection section with the two-folded portion serving as the leading edge, and the sheets are stacked on the tray. Alternatively, the sheets are ejected on a conveying unit and are conveyed with the aforementioned two-folded portion facing downstream in the conveying direction. The sheets are then stacked on the loading section downstream of the conveying unit.
The aforementioned sheet bundle is center-folded into two parts, as shown in FIG. 31. This increases the swelling of the portion of the sheet bundle S near the two-folded portion Sa.
In the meanwhile, as described above, when such a sheet bundle S is stacked on the tray or the loading section downstream of the conveying unit with the two-folded portion serving as a leading edge, the bulk on the leading edge increases excessively and the sheets tends to collapse. Thus, the loading capacity is reduced, that is, the quantity of the booklets produced in one operation will be restricted.
For this reason, in one of such post-processing apparatuses known in the conventional art, while the sheet bundle is stacked on the loading tray after being ejected out of the apparatus with the two-folded portion thereof serving as the leading edge, the sheet bundle is reversed by a reversing unit so that the two-folded portion is made to face upstream in the conveying direction, for example, as shown in the Japanese Unexamined Patent Application Publication No. 2002-87679.
In the post-processing apparatus disclosed in the aforementioned Japanese Unexamined Patent Application Publication No. 2002-87679, the sheet bundle ejected from the sheet ejection section with the two-folded portion serving as a leading edge is stacked on the loading tray and is reversed by the reversing unit so that the two-folded portion is made to face upstream in the conveying direction. However, the sheet bundle to be reversed does not have an interleaf SS in the free state in the center-folded sheet, that is, the interleaf is not inserted in the state where saddle stitching or center folding has not been carried out, as in the case of the sheet bundle S of FIG. 31.
The open/close end face arranged on the sheet ejection port in the form biased in the close direction, or the sheet ejection rollers wherein the peripheral speed of the upper roller is higher than that of the lower roller is used as the reversing unit. When the sheet bundle passes through the reversing unit, the leading edge of the sheet bundle is forcibly directed downward, and the sheet bundle falls onto the tray by the own weight, with the result that the two-folded portion faces upstream in the conveying direction.
Thus, when the sheet bundle has fallen onto the tray by the own weight with the two-folded portion facing downward, the two-folded portion is not always so reversed as to face upstream in the direction of conveyance. The two-folded portion may fall downstream in the direction of conveyance. There is no denying that sheet bundle reversing operation may become unstable.
Accordingly, especially when this method is applied to the post-processing apparatus for acquiring the sheet bundle wherein the interleaf has been inserted in the free state in the center-folded sheet, as described above, the stacked sheet bundles may contain some incorrectly reversed sheet bundles, or because of feeding in the incorrectly reversed state, the interleaves in the center-folded sheets may fall from the sheet bundle.
To avoid the incorrect reversing of the sheet bundle by the reversing unit, a proposal has been made to combine the aforementioned open/close end face and sheet ejection rollers wherein the peripheral speed of the upper and lower rollers are different from each other, and to additionally install a pushing member for pushing forward the upper side of the intermediate portion of this sheet bundle when the two-folded portion located on the downstream side of the sheet bundle having passed through the aforementioned open/close end face has reached the tray, in addition to the reversing component parts of the aforementioned open/close end face and sheet ejection rollers. However, this proposal increases the number and parts and raises a cost problem. Not only that, this proposal raises a control difficulty in keeping balance between the open/close operation of the open/close end face and the operation of the sheet ejection rollers and pushing member, with the result that the control system is complicated and the costs are further increased.
Thus, it is a further object of an embodiment of the present invention to provide a post-processing apparatus for ensuring that the fall of the interleaves having been inserted in the free state in the center-folded sheet is prevented in the process of stacking the sheet bundle subsequent to the sheet ejection and that sheet bundles are stacked in a standing and leaning position in an orderly manner without the shape of the sheet bundle being collapsed and the loading volume is increased.